Syrian President Bashar al-Assad has said he is committed to a plan to destroy his country's chemical weapons, but warned it could take about a year.

Speaking to Fox News, Mr Assad again denied claims that his forces were responsible for a deadly chemical attack near Damascus on 21 August.

The Syria disarmament plan was unveiled by the US and Russia last weekend.

The West wants the deal enshrined in a UN resolution backed by the threat of military force, but Russia objects.

Damascus - backed by Moscow - has insisted that rebel forces carried out last month's attack in the Ghouta area.

In separate developments, a roadside bomb attack in central Homs province caused multiple deaths and fierce fighting was reported between two rebel groups in the north of Syria.

The bomb detonated in the village of Jbourin as a convoy of minibuses was driving past. The UK-based Syrian Observatory for Human Rights said at least nine people were killed. Another report put the toll at 19.

Analysis

By Paul WoodBBC News, Turkish-Syrian border

The fighting over Azaz seems to have evolved accidentally, rather than having been part of a long-planned offensive. Still, there is a long record of skirmishing between jihadi militias and FSA brigades for control of the border crossings into Turkey (along with all the lucrative income from smuggling and stealing from aid shipments). Tensions between the two groups have been steadily escalating.

What does this mean for the Syrian revolution? In the long term, the United States and other Western governments might be more willing to support the Free Syrian Army if they see real distance between it and the jihadis. In the short term, if the rebels are fighting each other, they are not fighting the regime.

In the town of Azaz, near the Turkish border, jihadists from the al-Qaeda-linked group, the Islamic State in Iraq and Syria (Isis), reportedly clashed with fighters from the Western-backed Free Syrian Army (FSA).

Activists said on Thursday morning that Isis fighters had overrun the town in what is believed to be one of the biggest confrontations so far between the jihadists and the FSA.

The Syrian Observatory for Human Rights said the clashes erupted after a failed attempt to kidnap a German doctor working in the area.

Turkey closed one of its border gates to Syria near Azaz in response to the fighting, Reuters reported. The news agency quoted an official said the closure would disrupt the flow of humanitarian aid into Syria.

'Listen to your people'

Referring to the issue of destroying Syria's stockpiles of chemical weapons, Mr Assad said it was "a very complicated operation, technically".

"And it needs a lot of money, some estimates (say) about a billion [dollars].

"So it depends, you have to ask the experts what they mean by quickly. It has a certain schedule. It needs a year, or maybe a little bit more."

And when asked whether he would be willing to hand over chemical weapons to the US, President Assad said: "It needs about one billion. It is very detrimental to the environment. If the American administration is ready to pay this money and take the responsibility of bringing toxic materials to the United States, why don't they do it?"

'Very serious'

Mr Assad also used the one-hour interview recorded in Damascus to criticise the US stance in the Syrian crisis.

Unlike the Russians, he said, Washington had tried to get involved in Syria's leadership and governance.

He argued that if there was mutual respect, there would not be any problems.

"Listen to your people. Follow the common sense of your people," he said, in an apparent reference to US President Barack Obama.

Mr Assad's comments come shortly after a senior Russian diplomat said Damascus would fulfil its commitment to eliminate its chemical weapons by mid-2014.

After talks in Syria on Wednesday, Deputy Foreign Minister Sergei Ryabkov said President Assad was "very serious" about the disarmament plan.

Media captionVladimir Putin says he is "hopeful" that Syria will fulfil the international plan to destroy its chemical weapons

Mr Ryabkov also said that Syrian officials had handed him "material evidence" that showed the rebels were involved in the sarin attack last month, contradicting claims by the US that the regime was responsible.

And the Russian diplomat criticised the United Nations for being "one-sided" in its recent report on the attack - a claim the UN denied.

The report - prepared for UN weapons experts after a visit to Syria - did not apportion blame for the 21 August attack.

German chemical exports

Meanwhile Germany's Chancellor Angela Merkel has said in an interview on German television that chemicals exported to Syria which were capable of being used to make poison gas were used for civilian purposes.

The German government, responding to a request from a member of parliament, said 137 tonnes of two substances capable of being used to make the poison gas sarin were exported to Syria between 2002 and 2006.

But she added that officials were still trying to ascertain what use was made of chemicals exported after 2006 and before May 2011, when Germany imposed strict controls on exports to Syria.

More than 100,000 people have been killed since Syria's civil war began in early 2011, according to the UN.

Millions have fled the country and millions more have been left homeless.